Face-type commutators for electric motors have a plurality of electrically conductive bars pre-assembled on a commutator body. In some motor applications the commutators are immersed in dielectric fluids but are not limited to use in such applications.
In the past, diamond cutting tools have been used to finish flat face surfaces of such commutators to remove bar-to-bar dimensional irregularities to produce a uniform commutator surface.
Brush commutated electric motors which operate in dielectric fluids or the hard vacuum of outer space have very special problems related to the mating of contacting brush surface and commutator. These conditions require the use of an especially soft brush material which if not properly mated to the commutator will glaze and not carry the electrical current necessary for the motor to do its job. An improperly seated brush will have areas which carry too much current, which causes arcing and consequent pitting of the commutator, leading to early motor failure.
The prior finishing methods including use of diamond cutting tools can produce a surface roughness on the surface and edge burr condition that can increase motor brush run-in time and which may or may not achieve proper mating of the brush and commutator.
Prior art apparatus for grinding commutator surfaces to finish conductor segments of cylindrical type commutators is shown in U.S. Pat. Nos. 969,633 and 3,965,623. Such apparatus expose only a limited portion of the commutator bars to a limited peripheral edge of a grinder wheel and the grinding wheel is advanced along the depth of the commutator bars so as to minimize burr formation and as such does not solve the problem of burr formation at the break line between conductor bars arranged in a flat surface radial disposition.